1. Field of the Invention
Aspects of the present invention relate to an image forming apparatus, and more particularly, to an image forming apparatus to reduce accidents caused when a cover of the apparatus is opened.
2. Description of the Related Art
Generally, an image forming apparatus, for example, electrophotographic-type image forming apparatus, uses an electrophotographic printing scheme. The apparatus projects a laser beam onto a photoconductive drum, to form an electrostatic latent image, and converts the electrostatic latent image into a visible image, using a developer mounted to a developing apparatus. The visible image is transferred onto paper, and then fixed to the paper with heat and pressure. There are a variety of electrophotographic image forming apparatuses, for example, a laser beam printer (LBP), a duplicating machine, a facsimile, a multi-functional device, etc.
The image forming apparatus includes a power-supply unit to convert an AC power into a DC power, according to voltages of individual loads of an image forming engine. The image forming engine basically requires a low-voltage, power-supply voltage of about 24V, and a high-voltage, power-supply voltage of about 100 Kv. The power-supply unit provides a power-supply voltage of 5V to a control unit that controls the image forming operations.
If an after-sale (A/S) repairman or a user opens a cover rotatably connected to the front or lateral side of a main body of the apparatus, to inspect or maintain the image forming apparatus, the repairman or user may be in danger from a high voltage inside of the main body. For this purpose, the image forming apparatus includes a first switch and a second switch. If the cover is open, the first switch blocks the power-supply voltage of 5V from being applied from the power-supply unit to the control unit, and the second switch blocks the power-supply voltage of 24V from being applied from the power-supply unit to the image forming engine.
The first and second switches are simultaneously switched off, when the cover of the image forming apparatus is open, so that the power-supply voltages, applied to the control unit and the image forming engine, are blocked. As a result, the repairman or user can be protected from an electric shock.
However, while the cover is open, if the first and second switches are simultaneously switched off, and the power-supply voltages applied to the control unit and the image forming engine are simultaneously turned off, the image forming engine suddenly stops operation. This can result in the image forming apparatus being unstably powered off. For example, in the case of a developing process, if a high voltage for controlling a toner is not applied to the developing process of the image forming apparatus, the developing process stops operation. In this case, a developing roller of the developer does not immediately stop operation, but instead, continuously rotates by inertia, for a relatively long period of time. A carrier for carrying the toner and the toner are not controlled by the high voltage, so that the carrier and toner may leak out. The leaked carrier and toner pollutes inner parts of the image forming apparatus, such that the printing performance and the image quality may be seriously degraded. In addition, the fine structure of the surface of the photoconductive drum can be damaged, resulting in degraded printing performance, and a reduced lifetime of the apparatus. In addition, if the image forming apparatus suddenly stops operation, gears may be engage with each other, complicating the disassembly thereof. If the image forming apparatus suddenly stops operation, when paper is inserted under the roller, the paper may become jammed.
A representative image forming apparatus capable of solving the above-mentioned problems has been disclosed in Japanese Patent Laid-open No. 2006-030702, which is hereby incorporated by reference. The image forming apparatus disclosed in Japanese Patent Laid-open No. 2006-030702 includes a relay circuit as a delay circuit. The relay circuit allows a power-supply voltage, applied to an image forming engine, to be continuously applied to the image forming engine during a predetermined period of time, even though the cover is open. Therefore, the image forming apparatus allows the image forming engine to normally stop operation, and prevents the power-supply voltage from being applied to the image forming engine.
However, the above-mentioned conventional art disclosed in Japanese Patent Laid-open No. 2006-030702 requires the additional relay circuit, resulting in increased production costs circuit complexity.